In automated test systems, a “load board” often provides an electrical and mechanical interface between a circuit tester of the test system and a device under test (DUT). The load board usually takes the form of a printed circuit board having one or more DUT contactors and impedance matching circuits thereon. The contactor(s) serve to mechanically hold (and provide electrical connections to) a number of DUTs, while the impedance matching circuit(s) serve to electrically couple DUT(s) held by the contactors to circuitry of the circuit tester.
At times, test equipment such as an automated DUT handler or environmental control system needs to mate to the load board of an automated test system. In the past, this has been dealt with by requiring the exterior surface of the load board to be free of obstructions. This, in turn, has forced load board designers to confine bias and impedance matching circuit(s) of the load board to the underside of the load board. However, placement of impedance matching circuit(s) on the underside of a load board can introduce a variety of design hurdles, such as: 1) signal routes may be longer, thereby increasing the likelihood of signal delay, signal skew, and signal noise; 2) vias through the load board are needed, thereby causing signals to bend at right angles and likely introducing signal reflections (not to mention that vias are typically less desirable interconnects than signal traces; and 3) termination impedances cannot be placed as close to a DUT.